A toner that fluoresces in a visible light range when irradiated with ultraviolet rays, such as black light, is often used in applications such as document security. In general, high fluorescence visibility when irradiated with the black light is desirable in these applications.
Generally, commercially available paper contains brightening agents which are fluorescent. Such paper tends to emit blue fluorescence when irradiated with the black light. Thus, visibility of an image formed with fluorescing toner on such paper may be low when irradiated with the black light. Therefore, a toner that glows white with fluorescence under black light conditions would be useful to improve visibility of the toner image.
In applications, such as document security, a toner emitting white fluorescence under black light conditions is often used together with a toner that appears colored under visible light conditions. In this case, an image formed by the visible light toner and an image formed by the fluorescing toner must be arranged on the same paper surface. Therefore, the image formed only with the fluorescing toner is preferably not visible under visible light conditions. In other words, it is preferable for the fluorescing toner to be invisible under normal lighting conditions yet to glow brightly due to fluorescence under other lighting condition.